Russian authorities say a conscript has killed an officer and two soldiers before turning the gun on himself.
The Investigative Committee said a serviceman armed with an automatic rifle fired shots at a military field camp near the Volga city of Kostroma on August 26, killing three people.
Investigators said the conscript wounded two other servicemen and then committed suicide.
The Defense Ministry said personal reasons could be behind the attacks.
Hazing in the Russian army remains a major problem and sometimes leads to suicides or murders.
Rights campaigners accuse the military of seeking to cover up instances of bullying.